Catalytic bed space heaters are well known and use as a fuel either combustible gas, such as butane, natural gas (methane) or propane, or a gas-forming liquid hydrocarbon, such as gasoline or some other liquid which forms a combustible gas such as methyl alcohol. Such a catalytic space heater is compact, convenient and attractive for use in an enclosed living space.
Three principal difficulties have been experienced with such heaters, however. When used as unvented heaters they will not comply with most building, installation and use codes presently in existence. Furthermore, even when vented catalytic space heaters of prior designs such as the design shown in U.S. Pat. No. 3,963,414, could not pass certification tests that require proof that all combustion gases have been collected for removal from the living space without excessive heat loss. Finally, when attempts were made to utilize a higher speed exhaust blower motor to meet the certification test, the heating and fuel efficiency of the prior design catalytic space heater was significantly reduced by excessive withdrawal of heated air from the living space and by premature withdrawal of combustion gases from the burner surface. In addition, the use of a high speed blower motor resulted in unacceptably high noise levels. Moreover, with the prior design mentioned should for some reason the exhaust duct flow be even slightly restricted, the combustion gases spill from the heater collection into the living space. This can result from adverse wind conditions at the exhaust outlet or a partially blocked flue, both of which inhibit or reduce the rate of exhaust flow.
It will therefore be appreciated that there has been a significant need for a catalytic space heater for heating an enclosed living space which can collect and remove from the living space substantially all combustion gases of the heater, and do so without significantly reducing the efficiency of the heater. Furthermore, the heater should operate at a relatively low exhaust flow rate with an exhaust blower motor operating at a low enough speed that it does not produce excessive noise. In addition, it is important that the spillage point of the heater occur at a sufficiently low exhaust flow that operation of the heater is not adversely affected by normal wind conditions at the exhaust outlet or by a partially blocked flue which might inhibit or reduce the rate of exhaust flow. Similarly, the heater should be operable with a low exhaust flow so that under normal operation the exhaust flow is sufficient to prevent spillage, but yet need not be very high to avoid the conventional flow-sensing safety controls, which terminate the fuel flow to the bed if insufficient exhaust flow is sensed, causing frequent nuisance lockouts of the fuel flow. The present invention fulfills these needs and provides other related advantages.